Glass composition, glass fiber, glass cloth, and method for producing glass fiber

ABSTRACT

The present disclosure provides a novel glass composition that has a low permittivity and is suitable for mass production. A glass composition provided satisfies, in wt %, for example, 40≤SiO2≤60, 25≤B2O3≤45, 0&lt;Al2O3≤18, 0&lt;R2O≤5, and 0≤RO≤12, and satisfies at least one of: i) SiO2+B2O3≥80 and SiO2+B2O3+Al2O3≤99.9; and ii) SiO2+B2O3≥78, SiO2+B2O3+Al2O3≤99.9, and 0&lt;RO&lt;10. Another glass composition provided includes SiO2, B2O3, Al2O3, R2O, and 3&lt;RO&lt;8 at the same contents as the above, and satisfies SiO2+B2O3≥75 and SiO2+B2O3+Al2O3&lt;97, where R2O=Li2O+Na2O+K2O and RO=MgO+CaO+SrO.

TECHNICAL FIELD

The present invention relates to a glass composition, and a glass fiberand a glass cloth that are formed of the composition. The presentinvention further relates to a method for producing glass fiber.

BACKGROUND ART

One type of printed circuit board mounted in electronic devices is aboard formed of a resin, a glass fiber, an in organic filler, and anadditional material such as a curing agent or a modifying agent asnecessary. Also, some of printed wiring boards, which have no electroniccomponents installed, are constituted in the same manner as the aboveboard. Hereinafter, in the present description, both the printed circuitboard and the printed wiring board are referred to as a “printed board”.In such a printed board, the glass fiber functions as an insulator, as aheat-resistant material, and as a reinforcement of the board. The glassfiber is included in a printed board in the form of, for example, aglass cloth, which is produced by weaving a glass yarn constituted of aplurality of glass fibers bundled together. Also, a glass cloth isusually used, in printed boards, as a prepreg impregnated with a resin.In recent years, printed boards have been made thinner to meet thedemand for reducing the size of electronic devices and the demand forincreasing the degree of integration of printed boards to achieve a highperformance. To achieve a thinner printed board, a glass fiber having asmaller fiber diameter is needed. Furthermore, because for example of arapidly increasing demand for high-speed transmission of large volumesof data, a glass fiber for printed boards is required to have a lowpermittivity.

Glass is sometimes used also as an inorganic filler for use in printedboards. Typical examples of the inorganic filler include a glass flake.When a shaped glass material such as a glass flake is used as aninorganic filler in a printed board, the shaped material is required tohave the same properties as those of the glass fiber for printed boards,for example, a low permittivity.

Glass fibers formed of low-permittivity glass compositions are disclosedin Patent Literatures 1 to 5.

CITATION LIST Patent Literature

Patent Literature 1: JP S62-226839 A

Patent Literature 2: JP 2010-508226 A

Patent Literature 3: JP 2009-286686 A

Patent Literature 4: WO 2017/187471 A1

Patent Literature 5: WO 2018/ 216637 A1

SUMMARY OF INVENTION Technical Problem

A glass composition is required to have characteristic temperaturessuitable for mass production as well as to have a low permittivity. Onecharacteristic temperature of the glass composition important for massproduction of a glass fiber is a temperature T3 serving as the referencefor the forming temperature, that is, a temperature at which theviscosity is 10³ dPas. Temperatures T2 and T2.5 and a devitrificationtemperature TL also serve as indicators for determining whether theglass composition is suitable for mass production of a glass fiber.However, it is not easy to adjust the characteristic temperatures of aglass composition having a low permittivity.

In view of the above, the present invention aims to provide a novelglass composition that has a low permittivity and is suitable for massproduction.

Solution to Problem

The present invention provides a glass composition including, in wt %:

40≤SiO₂≤60;

25≤B₂O₃≤45;

5≤Al₂O₃≤15;

0<R₂O≤5; and

0<RO<15, wherein

the glass composition satisfies:

SiO₂+B₂O₃≥80; and/or

SiO₂+B₂O₃≥78 and 0<RO<10.

In the present specification, R₂O is at least one oxide selected fromLi₂O, Na₂O, and K₂O, and RO is at least one oxide selected from MgO,CaO, and SrO.

In another aspect, the present invention provides a glass compositionincluding, in wt %: 40≤SiO₂≤60;

25≤B₂O₃≤45;

0<Al₂O₃≤18;

0<R₂O≤5; and

0≤RO≤12, wherein

the glass composition satisfies at least one of:

i) SiO₂+B₂O₃≥80 and SiO₂+B₂O₃+Al₂O₃≤99.9; and

ii) SiO₂+B₂O₃≥78, SiO₂+B₂O₃+Al₂O₃≤99.9, and 0<RO<10.

In another aspect, the present invention provides a glass composition,including, in wt %:

40≤SiO₂≤60;

25≤B₂O₃≤45;

0<Al₂O₃≤18;

0<R₂O≤5; and

3<RO<8, wherein

the glass composition satisfies:

SiO₂+B₂O₃≥75; and

SiO₂+B₂O₃+Al₂O₃<97.

In another aspect, the present invention provides a glass composition,satisfying, in wt %, SiO₂+B₂O₃≥77, wherein

a permittivity at a frequency of 1 GHz is 4.4 or less,

a dielectric loss tangent at a frequency of 1 GHz is 0.007 or less, and

a temperature T2 at which a viscosity is 10² dPas is 1700° C. or less.

In another aspect, the present invention provides a glass compositionincluding, in wt %:

40≤SiO₂≤49.95;

25≤B₂O₃≤40;

10≤Al₂O₃≤20;

0.1≤R₂O≤2; and

1≤RO≤10, wherein

the glass composition satisfies:

SiO₂+B₂O₃≥70; and

SiO₂+B₂O₃+Al₂O₃≤97.

In another aspect, the present invention provides a glass compositionincluding, in wt %:

40≤SiO₂≤49.95;

25≤B₂O₃≤29.9;

10≤Al₂O₃≤20;

0.1≤R₂O≤1; and

2≤RO≤8, wherein

the glass composition satisfies:

SiO₂+B₂O₃≥70; and

SiO₂+B₂O₃+Al₂O₃≤97.

In another aspect, the present invention provides a glass compositionincluding, in wt %:

40≤SiO₂≤49.95;

31≤B₂O₃≤40;

8≤Al₂O₃≤18;

0.1≤R₂O≤1; and

1≤RO≤10, wherein

the glass composition satisfies:

SiO₂+B₂O₃≥77; and

SiO₂+B₂O₃+Al₂O₃≤97.

In yet another aspect, the present invention provides a glass fiberincluding the glass composition according to the present invention.

In yet another aspect, the present invention provides a glass clothincluding the glass fiber according to the present invention.

In yet another aspect, the present invention provides a prepregincluding the glass cloth according to the present invention.

In yet another aspect, the present invention provides a printed boardincluding the glass cloth according to the present invention.

In yet another aspect, the present invention provides a method forproducing glass fiber, the method including melting the glasscomposition according to the present invention at a temperature of 1400°C. or more to obtain a glass fiber having an average fiber diameter of 1to 6 μm.

Advantageous Effects of Invention

According to the present invention, it is possible to provide a glasscomposition that has a lower permittivity and has characteristictemperatures suitable for mass production.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the symbol “%” indicating the content of each componentmeans “wt %” in every case. The phrase “substantially free of” meansthat the content is less than 0.1 wt %, preferably less than 0.07 wt %,and more preferably less than 0.05 wt %. The term “substantially” inthis phrase is intended to allow impurities inevitably introduced fromindustrial raw materials within the above limits. The content,properties, and other preferred ranges of each component can beunderstood by arbitrarily combining the upper and lower limitsindividually described below.

In the following description, as the characteristic temperature of aglass composition, a temperature at which the viscosity is 10^(n) dPasis expressed as Tn (for example, T2.5 means a temperature at which theviscosity of the glass composition is 10^(2.5) dPas). Permittivityrefers to relative permittivity (dielectric constant) in a strict sense.In the present specification, relative permittivity is expressed simplyas permittivity, as is conventional. Values of permittivity anddielectric loss tangent are those determined at room temperature (25°C.). The following description is not intended to limit the presentinvention, and is provided in the sense of indicating preferredembodiments thereof.

[Components of Composition]

(SiO₂)

SiO₂ is a component forming a network structure of glass. SiO₂ acts todecrease the permittivity of a glass composition. An excessively lowSiO₂ content cannot sufficiently decrease the permittivity of the glasscomposition. An excessively high SiO₂ content excessively increases theviscosity at melting and thus a homogeneous glass composition isdifficult to obtain. A decrease in homogeneity of the glass compositioninduces fiber breakage of a glass fiber, particularly a glass fiberhaving a small fiber diameter, during fiber forming. The SiO₂ content ispreferably 40% or more, 45% or more, 46% or more, more preferably 48% ormore, and particularly preferably 49% or more, and may be, in somecases, 50% or more, even 50.5% or more, 51% or more, 52% or more, or 53%or more. The SiO₂ content is preferably 60% or less, less than 58%, 56%or less, more preferably less than 55%, and particularly preferably54.5% or less, and may be, in some cases, 54% or less, 53% or less, 52%or less, or 51% or less. An example of a preferred range of the SiO₂content is 40% or more and less than 58%, and even 40% or more and lessthan 55%. In addition, the SiO₂ content can be 40% or more and 49.95% orless.

(B₂O₃)

B₂O₃ is a component forming a network structure of glass. B₂O₃ acts todecrease the permittivity of the glass composition, and also acts todecrease the viscosity of the glass composition at melting to improvethe defoaming performance (bubble removability), thereby reducinginclusion of bubbles in the glass fiber formed. On the other hand, B₂O₃is prone to volatilization at melting of the glass composition. Anexcessively high content of B₂O₃ makes it difficult to achieve asufficient homogeneity of the glass composition, insufficiently reducesinclusion of bubbles in the glass fiber, or causes a so-called fiberbreakage due to deposition of B₂O₃ volatilized from glass on tips of abushing used for fiber forming. The B₂O₃ content is preferably 25% ormore, 27% or more, 29% or more, 30% or more, and more preferably morethan 30%, and may be, in some cases, 30.5% or more, even 31% or more,32% or more, 33% or more, or 34% or more. The B₂O₃ content is preferably45% or less, 43% or less, 41% or less, and more preferably 39% or less,and may be, in some cases, 38% or less, even 36% or less, 35% or less,34% or less, or 32% or less. An example of a preferred range of the B₂O₃content is more than 30% and 45% or less. In addition, the B₂O₃ contentcan be 25% or more and 40% or less, 25% or more and 29.9% or less, or31% or more and 40% or less.

(SiO₂+B₂O₃), (SiO₂+B₂O₃+Al₂O₃)

To obtain a glass composition having a sufficiently low permittivity,the total of the SiO₂ content and the B₂O₃ content, that is, (SiO₂+B₂O₃)may be adjusted to 77% or more, 78% or more, or even 80% or more.(SiO₂+B₂O₃) is preferably 81% or more, 82% or more, and more preferably83% or more, and may be, in some cases, 84% or more, or even 85% ormore. (SiO₂+B₂O₃) may be 90% or less, or even 87.5% or less. This isbecause an excessively high value of (SiO₂+B₂O₃) encourages the tendencyfor the glass composition to undergo phase separation. In addition,(SiO₂+B₂O₃) can be 70% or more. The total of the SiO₂ content, the B₂O₃content, and the Al₂O₃ content, that is, (SiO₂+B₂O₃+Al₂O₃) is suitably99.9% or less in order to allow additional components. (SiO₂+B₂O₃+Al₂O₃)may be 98% or less, 97% or less, less than 97%, or even 96% or less. Ina preferred example of a combination of (SiO₂+B₂O₃) and(SiO₂+B₂O₃+Al₂O₃), (SiO₂+B₂O₃) is 82% or more and (SiO₂+B₂O₃+Al₂O₃) is98% or less. Also, (SiO₂+B₂O₃+Al₂O₃) can be 90% or more and 98% or less,or 90% or more and 97% or less.

The ratio of (SiO₂+B₂O₃+Al₂O₃) to (SiO₂+B₂O₃), that is,(SiO₂+B₂O₃+Al₂O₃)/(SiO₂+B₂O₃) is preferably 1.05 or more, and may be1.12 or more, 1.13 or more, 1.15 or more, or 1.20 or more. As this ratioincreases, a defect such as fluffing of the glass fiber is reduced more.This effect becomes remarkable in a fifth combination of the SiO₂ andB₂O₃ contents described later.

(Preferred Combination of SiO₂ and B₂O₃)

To obtain a glass composition that has a lower permittivity and is easyto melt, there are combinations of the SiO₂ and B₂O₃ contents withinpreferred ranges. A first combination is a combination in which the SiO₂content is 48 to 51%, preferably 49 to 51%, and more preferably 50 to51%, and the B₂O₃ content is 33 to 35%, and preferably 34 to 35%. Asecond combination is a combination in which the SiO₂ content is 50 to53%, and preferably 51 to 52%, and the B₂O₃ content is 32 to 35%, andpreferably 32 to 34%. A third combination is a combination in which theSiO₂ content is 52 to 54%, and preferably 52.5 to 54%, and the B₂O₃content is 31 to 34%, and preferably 32 to 34%. A fourth combination isa combination in which the SiO₂ content is 52 to 55%, and preferably 53to 55%, and the B₂O₃ content is 30 to 32%.

A fifth combination is a combination in which the SiO₂ content is 47 to52%, preferably 48 to 51%, more preferably 48.5 to 50.5%, andparticularly preferably 48.95 to 49.95%, and the B₂O₃ content is 25 to30%, preferably 26 to 29.5%, and more preferably 26 to 29%. In the fifthcombination, the total of the MgO content and the CaO content, that is,(MgO+CaO) is suitably 3.5% or more, and more suitably 4% or more, and issuitably 8% or less. A sixth combination is a combination in which theSiO₂ content is 48 to 53%, preferably 49 to 52%, and more preferably 49to 51.5%, and is, in some cases, 49 to 51% or 48.95 to 49.95%, and theB₂O₃ content is 28 to 35%, and preferably 30 to 33%, and is, in somecases, 30.5 to 32.5%. In the sixth combination, (MgO+CaO) is 1% or moreand less than 3.5%, preferably 1 to 3%, and more preferably 1 to 2.5%,and is 1.5 to 2.5% in some cases.

(Al₂O₃)

Al₂O₃ is a component forming a network structure of glass. Al₂O₃ acts toenhance the chemical durability of the glass composition. On the otherhand, Al₂O₃ makes the glass composition more likely to sufferdevitrification during fiber formation. The Al₂O₃ content is preferably5% or more, 7.5% or more, 8% or more, 9% or more, and more preferably10% or more, and may be, in some cases, 10.5% or more, 12% or more, or13% or more. The Al₂O₃ content is preferably 20% or less, 18% or less,17% or less, and more preferably 15% or less, and may be, in some cases,14% or less, even 13% or less, or 12.5% or less. An example of the Al₂O₃content suitable for reliably controlling the devitrificationtemperature TL to fall within a range lower than the temperature T3 is12.3% or less. Al₂O₃ is generally understood to be a component thatincreases the viscosity of a glass composition at melting. However, in aglass composition having a high value of SiO₂+B₂O₃, Al₂O₃ can act todistinctively decrease the viscosity at melting.

An example of a preferred range of the Al₂O₃ content is 8 to 12.5%, andparticularly 10 to 12.5%. In the case where the above first to fourthcombinations of the SiO₂ and B₂O₃ contents are employed, these rangesare particularly suitable.

Another example of the preferred range of the Al₂O₃ content is 13 to17%. In the case where the above fifth combination of the SiO₂ and B₂O₃contents is employed, the Al₂O₃ content is particularly suitably 13 to17%. Still another example of the preferred range of the Al₂O₃ contentis 12 to 15%. In the case where the sixth combination of the SiO₂ andB₂O₃ contents is employed, the Al₂O₃ content is particularly suitably 12to 15%.

Alkali metal oxides are known as components acting to decrease theviscosity at melting, but an increase in content of such an alkali metaloxide increases the permittivity simultaneously. In contrast, in thepreferred glass composition according to the present invention, Al₂O₃acts to distinctively decrease the viscosity at melting, but its adverseeffect of increasing the permittivity is slight.

(MgO)

MgO is an optional component that decreases the viscosity of the glasscomposition at melting to reduce inclusion of bubbles in the glassfiber, thereby improving the homogeneity of the glass composition. TheMgO content may be 0.1% or more, 0.2% or more, even 0.5% or more, or0.6% or more, and may be, in some cases, 0.8% or more, or even 1° A ormore. The MgO content is preferably less than 10%, 8% or less, 7% orless, or 5% or less, and may be, in some cases, 3% or less, even 2% orless, or particularly 1.6% or less. To set the ratio to the CaO contentwithin an appropriate range, the MgO content is sometimes preferably1.7% or less, 1.5% or less, more preferably 1.2% or less, and 1% orless. However, depending on the content of additional components, theoptimum MgO content is sometimes 2% or more, for example 2 to 8%, even 2to 5%, or 3 to 5%. MgO has a great effect of decreasing thedevitrification temperature, but does not increase the permittivity asmuch as an alkali metal oxide R₂O. Accordingly, it is preferable to addMgO in preference to R₂O, in other words, such that the MgO content ishigher than the R₂O content.

An example of a preferred range of the MgO content is 0.5 to 2%. In thecase where the first to fourth combinations of the SiO₂ and B₂O₃contents are employed, the MgO content is particularly suitably 0.5 to2% and even 0.5 to 1.6%. In the case where the fifth combination of theSiO₂ and B₂O₃ contents is employed, the MgO content is particularlysuitably 0.5 to 2% and even 1 to 2%. Another example of the preferredrange of the MgO content is 0.1 to 1%. In the case where the sixthcombination of the SiO₂ and B₂O₃ contents is employed, the MgO contentis particularly suitably 0.1 to 1% and even 0.1% or more and less than1%.

(CaO)

CaO is an optional component that improves the meltability of a glassraw material to decrease the viscosity of the glass composition atmelting. The action of CaO is more significant than that of MgO. The CaOcontent may be 0.1% or more, 0.5% or more, or even 1% or more, and maybe, in some cases, 1.5% or more, or even 2% or more. The CaO content ispreferably less than 10%, 7% or less, and 5% or less, and may be, insome cases, 4% or less, 3.5% or less, 3% or less, or even 2.5% or less.CaO has a great effect of increasing the permittivity of the glasscomposition compared with MgO and ZnO. For the same reason as MgO, it ispreferable to add CaO likewise in preference to an alkali metal oxideR₂O, in other words, such that the CaO content is higher than that theR₂O content.

An example of a preferred range of the CaO content is 2 to 5%, and even2 to 3.5%. In the case where the first to fifth combinations of the SiO₂and B₂O₃ contents are employed, the CaO content is particularly suitably2 to 5%. For the first to fourth combinations, 2 to 3.5% is moresuitable. For the fifth combination, 2.5 to 5% is more suitable. Anotherexample of the preferred range of the CaO content is 0.5 to 2%. In thecase where the sixth combination of the SiO₂ and B₂O₃ contents isemployed, the CaO content is particularly suitably 0.5 to 2%.

An example of a particularly preferred combination of the MgO contentand the CaO content is a combination in which the MgO content is 1 to 2%and the CaO content is 2 to 5%. This combination is particularlysuitable in the case where the fifth combination of the SiO₂ and B₂O₃contents is employed.

(SrO)

SrO is also an optional component that improves the meltability of aglass raw material to decrease the viscosity of the glass composition atmelting. However, SrO increases the permittivity of the glasscomposition compared with MgO and CaO, and accordingly it is desirableto limit the SrO content. The SrO content is preferably 1% or less, 0.5%or less, and more preferably 0.1% or less. The glass composition may besubstantially free of SrO.

In the case where the first to fifth combinations of the SiO₂ and B₂O₃contents are employed, the SrO content is particularly suitably 0.1% orless. In this case, the glass composition may be substantially free ofSrO. However, there is a case where SrO may be added such that the SrOcontent is 0.1 to 5%, and even 1 to 3.5%. In the case where the sixthcombination of the SiO₂ and B₂O₃ contents is employed, the SrO contentis particularly suitably 0.1 to 5% and even 1 to 3.5%. In particularlythe sixth combination, it has been found that SrO can effectively act todecrease the dielectric loss, in other words, to decrease the dielectricloss tangent, contrary to technical common sense of a person skilled inthe art. In the sixth combination, SrO/CaO representing the ratio of theSrO content to the CaO content may exceed 1. In this case, CaO/MgOrepresenting the ratio of the CaO content to the MgO content also mayexceed 1.

(RO)

The RO content, that is, the total of the contents of MgO, CaO and SrOis preferably less than 15%, 12% or less, 10% or less, less than 10%,9.5% or less, 8% or less, more preferably less than 7%, and particularlypreferably 6% or less, and may be, in some cases, 5% or less, or even 4%or less. An excessively high RO content may insufficiently decrease thepermittivity. Although the components constituting RO are eachindividually an optional component, it is preferable that at least oneof the components should be contained, that is, the total of thecontents of the components should exceed 0%. The RO content ispreferably 1% or more, 1.5% or more, 2% or more, and more preferably2.5% or more, and may be, in some cases, 3% or more, or even 3.5% ormore.

A preferred example of a range of the RO content is 2 to 7%, andparticularly 2 to 4%.

(MgO/RO)

MgO/RO, that is, the ratio of the MgO content to the RO content ispreferably less than 0.8, and more preferably less than 0.7, and may be,in some cases, 0.5 or less, or 0.4 or less. When MgO/RO increases, thetendency for the glass composition to undergo phase separation becomesremarkable, and thus the homogeneity of the glass composition may beimpaired. In addition, fiber forming may become difficult due to amixture of phases differing in physical properties from each other. Onthe other hand, to decrease the permittivity of the glass composition,MgO/RO is preferably 0.1 or more, and more preferably 0.14 or more, andmay be 0.19 or more in some cases. MgO/RO is preferably 0.1 to 0.5.

(MgO/(MgO+CaO))

MgO/(MgO+CaO), that is, the ratio of the MgO content to the total of theMgO and CaO contents may also fall within a range of any combination ofthe upper and lower limits described above for MgO/RO. MgO/(MgO+CaO) ispreferably 0.1 to 0.5, and particularly preferably 0.1 to 0.4.

(Li₂O)

Li₂O is an optional component that, even when added in a small amount,acts to decrease the viscosity of the glass composition at melting toreduce inclusion of bubbles in the glass fiber, and further acts toreduce devitrification. Also, addition of Li₂O in an appropriate amountremarkably reduces the tendency for the glass composition to undergophase separation. However, Li₂O increases the permittivity of the glasscomposition although its action is relatively weaker than that of otherR₂O. The Li₂O content is preferably 1.5% or less, 1% or less, and 0.5%or less, and may be, in some cases, 0.4% or less, 0.3% or less, or even0.2% or less. The Li₂O content is preferably 0.01% or more, 0.03% ormore, and more preferably 0.05% or more. An example of a preferred rangeof the Li₂O content is 0.01 to 0.5%, and even 0.05 to 0.4%.

(Na₂O)

Na₂O is also an optional component that, even when added in a smallamount, acts to decrease the viscosity of the glass composition atmelting to reduce inclusion of bubbles in the glass fiber, and furtheracts to reduce devitrification. From this viewpoint, the Na₂O contentmay be 0.01% or more, 0.05% or more, or even 0.1% or more. However,addition of Na₂O needs to be kept within a limited range so as not toincrease the permittivity of the glass composition. The Na₂O content ispreferably 1.5% or less, 1% or less, 0.5% or less, and more preferably0.4% or less, and may be, in some cases, 0.2% or less, even 0.15% orless, particularly 0.1% or less, 0.05% or less, or 0.01% or less. Anexample of a preferred range of the Na₂O content is 0.01 to 0.4%.

(K₂O)

K₂O is also an optional component that, even when added in a smallamount, acts to decrease the viscosity of the glass composition atmelting to reduce inclusion of bubbles in the glass fiber, and furtheracts to reduce devitrification. However, K₂O significantly acts toincrease the permittivity of the glass composition. The K₂O content ispreferably 1% or less, 0.5% or less, and 0.2% or less, and may be, insome cases, 0.1% or less, 0.05% or less, or 0.01% or less. The glasscomposition may be substantially free of K₂O.

(R₂O )

The total of the R20 content and the Li₂O, Na₂O, and K₂O contents ispreferably 5% or less, 4% or less, 3% or less, 2% or less, and morepreferably 1.5% or less, and may be, in some cases, 1% or less, even0.6% or less, or 0.5% or less. Although the components constituting R₂Oare each individually an optional component, it is preferable that atleast one of the components should be contained, that is, the total ofthe contents of the components should exceed 0%. The R₂O content ispreferably 0.03% or more, 0.05% or more, more preferably 0.1% or more,particularly preferably 0.15% or more, and 0.2% or more.

Further, in the case where the Li₂O content is higher than the Na₂Ocontent, the tendency for the glass composition to undergo phaseseparation may be more effectively reduced.

When the Li₂O content is set to 0.25% or more or even 0.3% or more, thecharacteristic temperature sometimes can be adjusted to fall within amore preferred range. In particular, in the case where the firstcombination of the SiO₂ and B₂O₃ contents is employed, it is preferableto add Li₂O such that the Li₂O content is 0.25% or more or even 0.3% ormore. In this case, Na₂O may be added such that the Na₂O content is0.05% or more and less than the Li₂O content.

(T-Fe₂O₃)

T-Fe₂O₃ is an optional component that improves the meltability of theglass raw material owing to its heat absorbing action, and improves thehomogeneity of the glass composition at melting. The effect ofhomogeneity improvement by T-Fe₂O₃ reduces occurrence of fiber breakageof a glass fiber during fiber forming even when the glass fiber to beformed has a small fiber diameter, thereby improving the formingworkability. The T-Fe₂O₃ content is preferably 0.01% or more, 0.02% ormore, 0.05% or more, and more preferably 0.10% or more. The effect ofimproving the meltability is remarkably exhibited when the T-Fe₂O₃content is 0.01% or more. Meanwhile, the effect of improving thehomogeneity is particularly remarkably exhibited when the T-Fe₂O₃content is 0.02% or more. For the purpose of, for example, reducing anexcessive heat absorbing action exhibited by T-Fe₂O₃, the T-Fe₂O₃content is preferably 0.5% or less, 0.3% or less, and more preferably0.25% or less, and may be 0.20% or less in some cases. In the presentspecification, as is conventional, the amount of total iron oxide in theglass composition is expressed as a value obtained by converting ironoxides other than Fe₂O₃ such as FeO into Fe₂O₃, that is, as the T-Fe₂O ₃content. Accordingly, at least a portion of T-Fe₂O₃ may be contained asFeO. An example of a preferred range of the T-Fe₂O₃ content is 0.01 to0.5%, and even 0.1 to 0.3%.

(ZnO)

ZnO is an optional component that improves the meltability of the glassraw material to decrease the viscosity of the glass composition atmelting. However, ZnO increases the permittivity of the glasscomposition. The ZnO content is preferably 3.5% or less, 2% or less, 1%or less, and more preferably 0.5% or less. The glass composition may besubstantially free of ZnO.

(Additional Components)

Example of components that can be contained in the glass composition, inaddition to the above components, include P₂O₅, BaO, PbO, TiO₂, ZrO₂,La₂O₃, Y₂O₃, MoO₃, WO₃, Nb₂O₅, Cr₂O₃, SnO₂, CeO₂, As₂O₃, Sb₂O₃, and SO₃.Other components that can be contained in the glass composition include,for example, noble metal elements such as Pt, Rh, and Os, and, forexample, halogen elements such as F and Cl. The allowable content ofeach of these components is preferably less than 2%, more preferablyless than 1%, and particularly preferably less than 0.5%, and the totalcontent of the components is preferably less than 5%, more preferablyless than 3%, particularly preferably less than 2%, and moreparticularly preferably less than 1%. However, the glass composition maybe substantially free of each of the above additional components.Although a minute amount of TiO₂ may be added for the reasons describedbelow, the glass composition may be substantially free of TiO₂. The sameapplies to ZrO₂. In addition, it is preferable that the glasscomposition should be substantially free of BaO and PbO. It is alsopreferable that the glass composition should be substantially free ofP₂O₅. This is because BaO and PbO have a great effect of increasing thepermittivity of the glass composition, and P₂O₅ induces phaseseparation. The glass composition may be substantially free ofcomponents other than the components from SiO₂ to ZnO listed above.However, even in this case, the glass composition may contain componentsthat are effective in facilitating refining at melting, preferably SO₃,F, and Cl that are each within a range less than 2%.

It has been found that addition of a minute amount of TiO₂ sometimesdecreases the permittivity and the dielectric loss tangent of the glasscomposition, contrary to technical common sense of a person skilled inthe art. From this viewpoint, the TiO₂ content may be more than 0% and1% or less. In particular, in the case where the sixth combination ofthe SiO₂ and B₂O₃ contents is employed, TiO₂ may be added at a contentof more than 0% and 1% or less.

(Example of Preferred Composition)

In a preferred embodiment, the glass composition of the presentinvention includes the following components:

40≤SiO₂<58;

25≤B₂O₃≤40;

7.5≤Al₂O₃≤18;

0<R₂O≤4;

0≤Li₂O≤1.5;

0≤Na₂O≤1.5;

0≤K₂O≤1;

1≤RO<10;

0≤MgO<10;

0≤CaO<10;

0≤SrO≤5; and

0≤T-Fe₂O₃≤0.5.

In an embodiment including the above components, the following may besatisfied:

7.5≤Al₂O₃≤15; and

0≤SrO≤1.

A glass composition in which the following is added to the end of theabove relationships is also another preferred embodiment:

0≤ZnO≤3.5.

The glass compositions of these embodiments preferably further satisfy40≤SiO₂<55. Also, the glass compositions may satisfy SiO₂+B₂O₃≥80, andmay preferably further satisfy SiO₂+B₂O₃+Al₂O₃≤99.9. MgO/RO<0.8 is alsoother conditions that the glass compositions of the above embodimentsmay satisfy.

[Properties]

(Permittivity)

In a preferred embodiment, the permittivity of the glass compositionaccording to the present invention at a measurement frequency of 1 GHzis 4.65 or less, 4.4 or less, 4.35 or less, 4.30 or less, 4.25 or less,or even 4.20 or less, and is 4.18 or less in some cases. Thepermittivity at a measurement frequency of 5 GHz is 4.63 or less, 4.4 orless, 4.31 or less, 4.27 or less, 4.22 or less, or even 4.17 or less,and is 4.15 or less in some cases. The permittivity at a measurementfrequency of 10 GHz is 4.55 or less, 4.4 or less, 4.22 or less, 4.18 orless, 4.14 or less, or even 4.08 or less, and is 4.06 or less in somecases.

(Dielectric Loss Tangent: tan δ)

In a preferred embodiment, the dielectric loss tangent of the glasscomposition according to the present invention at a measurementfrequency of 1 GHz is 0.007 or less, 0.005 or less, 0.004 or less, oreven 0.003 or less, and is 0.002 or less in some cases. The dielectricloss tangent at a measurement frequency of 1 GHz may be 0.001 or less,less than 0.001, 0.0009 or less, 0.0008 or less, or even 0.0007 or less.The dielectric loss tangent at a measurement frequency of 5 GHz is 0.007or less, 0.005 or less, 0.004 or less, or even 0.003 or less, and is0.002 or less in some cases. The dielectric loss tangent at ameasurement frequency of 10 GHz is 0.007 or less, 0.006 or less, 0.005or less, 0.004 or less, or even 0.003 or less, and is 0.002 or less insome cases.

(Characteristic Temperature)

In a preferred embodiment, T2 of the glass composition according to thepresent invention is 1700° C. or less, 1650° C. or less, 1640° C. orless, 1620° C. or less, or even 1610° C. or less, and is, in some cases,less than 1600° C., 1550° C. or less, even 1520° C. or less, orparticularly 1510° C. or less. T2 is a temperature serving as thereference for the melting temperature of the glass melt. An excessivelyhigh T2 requires an extremely high temperature for melting the glassmelt, and thus causes a high energy cost and a high cost of apparatusesresistant to high temperatures. When molten at the same temperature, aglass having a lower T2 has a lower viscosity of the melt, andaccordingly is effective in refining and homogenizing the glass melt.Meanwhile, when molten at the same viscosity, a glass having a lower T2can be molten at a lower temperature, and accordingly is suitable formass production. T2.5 is preferably 1590° C. or less, 1550° C. or less,and more preferably 1500° C. or less, and is, in some cases, 1450° C. orless, or even 1400° C. or less. T3 is preferably 1450° C. or less, 1420°C. or less, 1400° C. or less, more preferably 1365° C. or less, andparticularly preferably 1360° C. or less, and is, in some cases, 1330°C. or less, or even 1300° C. or less. T3 is a temperature serving as thereference for the forming temperature of a glass fiber. An excessivelyhigh T3 increases B₂O₃ volatilizing from glass on tips of a bushing anddepositing on the tips, and thus may increase a risk of a so-calledfiber breaking.

In a preferred embodiment, T3 of the glass composition according to thepresent invention is higher than the devitrification temperature TL. Inaddition, in a more preferred embodiment, T3 is higher than TL by 10° C.or more, by even 50° C. or more, and, in some cases, by 100° C. or more.In a preferred embodiment, T2.5 of the glass composition according tothe present invention is higher than the devitrification temperature TLby 50° C. or more. In addition, in a more preferred embodiment, T2.5 ishigher than TL by 100° C. or more. T3 and T2.5 that are sufficientlyhigher than TL significantly contribute to the stable production of aglass fiber.

The fifth combination of the SiO₂ and B₂O₃ contents is particularlysuitable for achieving a preferred characteristic temperature. Thepreferred characteristic temperature is, for example, T2 that is 1520°C. or less, particularly 1510° C. or less, and is also, for example, T3that is 1300° C. or less and higher than TL. A glass composition havingan Li₂O content of 0.25% or more in the first combination of the SiO₂and B₂O₃ contents is also suitable as much as the above for achievingthe preferred characteristic temperature.

[Applications]

The applications of the glass composition according to the presentinvention are not limited. Application examples include a glass fiberand shaped glass materials. Examples of the shaped glass materialsinclude a glass flake. That is, the glass composition of the presentinvention can be a glass composition for a glass fiber, a glasscomposition for shaped glass materials, or a glass composition for aglass flake.

The glass composition according to the present invention is a glasscomposition with which occurrence of devitrification and inclusion ofbubbles in a glass fiber to be formed can be further reduced even whenthe glass fiber has a small fiber diameter. Here, the phrase “glassfiber having a small fiber diameter” means, for example, a glass fiberhaving an average fiber diameter of 1 to 6 μm. That is, the glasscomposition according to the present invention can be a glasscomposition for a small-diameter glass fiber, and more specifically, canbe a glass composition for a glass fiber having an average fiberdiameter of 1 to 6 μm. In addition, as described above, the effect ofthe present invention becomes more remarkable when a glass fiberproduced from the glass composition according to the present inventionis used in printed boards. From this viewpoint, the glass compositionaccording to the present invention can be a glass composition for aglass fiber for use in printed boards (printed wiring boards and printedcircuit boards).

Likewise, the glass composition according to the present invention is aglass composition with which occurrence of devitrification and inclusionof bubbles in a shaped glass material to be formed such as a glass flakecan be further reduced even when the shaped glass material has a smallthickness. Here, the term “small thickness” means, for example, 0.1 to2.0 μm. In addition, as described above, the effect of the presentinvention becomes more remarkable when a shaped glass material producedfrom the glass composition of the present invention (a shaped glassmaterial formed of the glass composition according to the presentinvention) is used in printed boards. From this viewpoint, the glasscomposition according to the present invention can be a glasscomposition for shaped glass materials for use in printed boards.

In view of the usability in printed boards, the glass compositionaccording to the present invention can be a glass composition forprinted boards.

[Glass Fiber]

The glass fiber according to the present invention are formed of theglass composition according to the present invention. The details of theglass fiber are not particularly limited, and the glass fiber can beconstituted in the same manner as conventional glass fibers as long asthe glass fiber is formed of the glass composition according to thepresent invention. As described above, the glass composition accordingto the present invention is a low-permittivity glass composition withwhich occurrence of devitrification and inclusion of bubbles in a glassfiber to be formed can be further reduced even when the glass fiber hasa small fiber diameter, and thus the glass fiber according to thepresent invention can be a glass fiber having a small fiber diameter.Also, such a fiber having a low permittivity and a small fiber diameteris an embodiment of the glass fiber according to the present invention.

The average fiber diameter of the glass fiber may be, for example, 1 to10 μm or even 6 to 10 μm, or may be 1 to 6 μm. The average fiberdiameter may be 3 μm or more, or may be 10 μm or less, 5.1 μm or less,4.6 μm or less, or even 4.3 μm or less. A glass composition havingcharacteristic temperatures suitable for mass production is suitable forstable production of a thin glass fiber. In a preferred embodiment, theaverage fiber diameter is even smaller, and is, for example, 3.9 μm orless, or even 3.5 μm or less. The glass fiber is, for example, acontinuous glass fiber (filament).

Preferred applications of the glass fiber according to the presentinvention include printed boards. A glass fiber having a lowpermittivity and a small fiber diameter is suitable for use in printedboards. However, the applications are not limited to printed boards.

The glass fiber can be formed into a glass yarn. The glass yarn caninclude a glass fiber other than the glass fiber according to thepresent invention, and may be formed only of the glass fiber accordingto the present invention, specifically that in the form of a continuousglass fiber. This glass yarn has a reduced occurrence of a defect suchas fiber breakage or fluffing of the glass fiber, and exhibits a highproductivity.

The number of continuous glass fibers (the number of filaments) includedin a glass yarn is, for example, 30 to 400. In the case of use inprinted boards, the number of filaments may be, for example, 30 to 120,30 to 70, or even 30 to 60. An appropriate number is advantageous informing a glass cloth more easily and reliably and achieving a thinnerprinted board. However, the structure and applications of the glass yarnare not limited to these examples.

The glass yarn including the glass fiber may have a count of, forexample, 0.7 to 6 tex, 0.9 to 5 tex, even 1 to 4 tex, even 1 to 3 tex,or 10 to 70 tex. An appropriate count is advantageous in forming a thinglass cloth more easily and reliably and achieving a thinner printedboard.

The glass yarn may have a strength of 0.4 N/tex or more, even 0.6 N/texor more, or particularly 0.7 N/tex or more.

The glass fiber according to the present invention can be produced byapplying a known method. For example, when a glass fiber having anaverage fiber diameter of about 1 to 6 μm is produced, the followingexemplary method can be employed. Specifically, the glass compositionaccording to the present invention is placed in a glass melting furnaceand molten into molten glass, and then the molten glass is drawn througha large number of forming nozzles provided at the bottom of aheat-resistant bushing of a drawing furnace, and thus to be shaped intofibers. In this manner, the glass fiber formed of the glass compositionaccording to the present invention can be produced. The glass fiber canbe a continuous glass fiber (filament). The melting temperature in themelting furnace is, for example, 1300 to 1700° C., preferably 1400 to1700° C., and more preferably 1500 to 1700° C. In these cases, even whena glass fiber to be formed has a small fiber diameter, occurrence offine devitrification and inclusion of bubbles in the glass fiber can befurther reduced and, in addition, an excessive increase in formingtension can be prevented, so that the properties (such as strength) andthe quality of the resulting glass fiber are reliably ensured.

To produce a glass fiber having a small fiber diameter, the followingapproaches are also possible, including an approach of increasing thedrawing rate of molten glass from a drawing furnace and an approach ofdecreasing the temperature of forming nozzles. However, the formerapproach sometimes fails to allow a sufficient time for facilitatingdefoaming of molten glass in the drawing furnace. This may cause, forexample, fiber breakage during fiber forming due to inclusion ofbubbles, or a decrease in strength of a fiber. Additionally, theincrease in drawing rate entails an increase in the tension (formingtension) acting on a fiber during fiber forming, and this increasedtension may also cause fiber breakage during fiber forming, a decreasein strength of the fiber, a degradation in quality of the fiber, and thelike. To wind a glass fiber, a winding rotary apparatus called collet isused usually. An excessive increase in forming tension causes the woundglass fiber to have kinks due to recesses between fingers, and thisleads to a degradation in quality of the glass fiber. Note that thecollet is an apparatus provided with a plurality of fingers on the outerperiphery of its main body, and the fingers move outwardly in the radialdirection of the collet during rotation of the collet, and sink into themain body of the collet while the collet is at rest. The degradation inquality of the glass fiber may lead to, for example, poor appearanceand/or fiber-opening failure of a glass cloth. Meanwhile, the latterapproach requires decreasing the melting temperature in the meltingfurnace as well. This makes the melting temperature closer to thedevitrification temperature of the glass composition, and accordinglyincreases the viscosity of the molten glass, which may fail to performsufficient defoaming. The forming tension also increases with theincrease in viscosity, and thus the above problems may occur.

By using the glass composition according to the present invention formelting in the above temperature ranges, it is possible to alleviate theabove problems. An improvement in quality of a glass fiber results ingood appearance and/or high degree of fiber opening of a glass clothproduced using the glass fiber.

A glass strand can be formed by applying a sizing agent to the surfacesof formed glass fibers and bundling together a plurality of such glassfibers, for example, 10 to 120 glass fibers. This strand includes theglass fiber according to the present invention. A glass yarn can beformed by winding the strands around a tube (for example, a paper tube)on a collet rotating at a high speed to form a cake, then unwinding thestrands from the outer layer of the cake, twisting the strands under airdrying, winding the strands around a bobbin or the like, and furthertwisting the strands.

[Glass Cloth]

The glass cloth according to the present invention is formed of theglass fiber according to the present invention. The glass clothaccording to the present invention can also have the above properties,such as a low permittivity, the glass composition according to thepresent invention has. The weave of the glass cloth according to thepresent invention is, for example, plain weave, satin weave, twillweave, mat weave, or rib weave, and is preferably plain weave. However,the weave is not limited to these examples. A glass cloth can include aglass fiber other than the glass fiber according to the presentinvention, but may be formed only of the glass fiber according to thepresent invention, specifically that in the form of a continuous glassfiber. The glass cloth according to the present invention has a reducedoccurrence of a defect such as fiber breakage or fluffing of the glassfiber, and also exhibits a high productivity.

In a preferred embodiment, the thickness of the glass cloth ispreferably 200 μm or less, more preferably 7 to 150 μm, even morepreferably 7 to 30 μm, and particularly preferably 8 to 15 μm, asexpressed by a thickness measured according to 7.10.1 of JIS R 3420:2013. The glass cloth of the preferred embodiment is suitable forachieving a thinner printed board.

In a preferred embodiment, the mass of the glass cloth is preferably 250g/m² or less, more preferably 150 g/m² or less, even more preferably 50g/m², and particularly preferably 15 g/m² or less, as expressed by across mass measured according to 7.2 of JIS R 3420: 2013. The glasscloth of the preferred embodiment is suitable for use in thinner printedboards.

In a preferred embodiment, the number of glass fibers per unit length(25 mm) in the glass cloth (weave density) is, for example, preferably40 to 130, more preferably 60 to 120, and even more preferably 90 to120, per 25 mm for both warps and wefts. The glass cloth of thepreferred embodiment is suitable for reducing its thickness, andincreasing the number of interlacing points between warps and wefts toreduce the likelihood of bias or bowed filling of the glass cloth toreduce generation of pinholes in impregnation with a resin.

In a preferred embodiment, the air permeability of the glass cloth is,for example, 400 cm³/(cm²·sec) or less, preferably 300 cm³/(cm²·sec) orless, and more preferably 250 cm³/(cm²·sec) or less. The glass cloth ofthe preferred embodiment is suitable for reducing its thickness toreduce the generation of pinholes described above. To achieve fiberopening that allows the glass cloth to have an air permeability similarto the above, the glass fiber may be obtained by applying the meltingtemperature described above, that is, 1400° C. or more, preferably 1400to 1650° C., to the glass composition according to the presentinvention, or to a glass raw material prepared such that the glasscomposition according to the present invention is obtained from theglass raw material.

The glass cloth according to the present invention can be produced usingthe glass fiber according to the present invention by a known method.One of exemplary producing methods is a method in which glass yarns aresubjected to warping and sizing, and then the resulting glass yarns areused as warp yarns, between which other glass yarns are inserted as weftyarns. For weft insertion, various weaving machines can be used, such asa jet loom, a Sulzer loom, and a rapier loom. Specific examples of thejet loom include an air-jet loom and a water-jet loom. However, theweaving machine for producing the glass cloth is not limited to these.

The glass cloth according to the present invention may be subjected tofiber opening. Fiber opening is advantageous in achieving a thinnerglass cloth. The details of the method for fiber opening are notparticularly limited, and examples of applicable methods include fiberopening by pressure of water stream, fiber opening by high-frequencyvibration using water or the like as a medium, and fiber opening bycompression using rolls or the like. Examples of the water usable as themedium for fiber opening include degassed water, ion-exchanged water,deionized water, electrolyzed cation water, and electrolyzed anionwater. Fiber opening may be performed simultaneously with or afterweaving of the glass cloth. Also, the fiber opening may be performedsimultaneously with or after other various treatments such as heatcleaning and surface treatment.

When a substance such as a sizing agent remains attached to the wovenglass cloth, a removal treatment on the substance, typified by heatcleaning treatment, may be performed additionally. When used in printedboards, the glass cloth subjected to the removal treatment exhibits anexcellent impregnability with a matrix resin and an excellent adhesionto the resin. After or separately from the removal treatment, the wovenglass cloth may be subjected to a surface treatment with a silanecoupling agent or the like. The surface treatment can be performed by aknown method, specifically by a method in which a silane coupling agentis impregnated into, spread over, or sprayed onto the glass cloth.

The glass cloth according to the present invention is suitable forprinted boards. In the case of use in printed boards, it is possible toeffectively utilize the feature of the glass cloth that can be formed ofa glass fiber having a low permittivity and a small fiber diameter.However, the applications are not limited to printed boards.

Prepreg

The prepreg according to the present invention can be formed of theglass cloth according to the present invention. The prepreg according tothe present invention can also have the above properties, such as a lowpermittivity, the glass composition according to the present inventionhas. The method for producing the prepreg of the present invention isnot particularly limited, and any conventionally known producing methodmay be employed. A resin to be impregnated into the prepreg according tothe present invention is not particularly limited as long as it is asynthetic resin that can be composited with the glass cloth of thepresent invention. Examples of the resin include thermosetting resins,thermoplastic resins, and composite resins thereof. It is desirable touse a resin having a low permittivity corresponding to a lowpermittivity of the glass cloth according to the present invention.

Printed Board

The printed board according to the present invention can be formed ofthe glass cloth according to the present invention. The printed boardaccording to the present invention can also have the above properties,such as a low permittivity, the glass composition according to thepresent invention has. The method for producing the board of the presentinvention is not particularly limited, and any conventionally knownproducing method may be employed. In an exemplary producing method, aprepreg including a resin impregnated into a glass cloth is produced andthen is cured.

EXAMPLES

Hereinafter, the present invention will be described in more detail byExamples. The present invention is not limited to the followingExamples.

Glass raw materials were weighed to give each composition shown inTables 1 to 6 (the contents of the components are expressed in wt %),and were mixed to homogeneity. Thus, a glass raw material mixture batchwas produced. Next, the produced mixture batch was introduced into acrucible made of platinum-rhodium alloy, and heated in anindirect-heating electric furnace set at 1600° C. in an air atmospherefor 3 hours or more to obtain a molten glass. Next, the obtained moltenglass was poured into a fire-resistant mold to be cast-molded. Theresulting shaped body was then cooled slowly to room temperature by anannealing furnace to obtain glass composition samples to be used forevaluation.

The glass samples thus produced were evaluated for the characteristictemperatures T2, T2.5, and T3, the devitrification temperature TL, andthe permittivity and the dielectric loss tangent at frequencies of 1GHz, 5 GHz, and 10 GHz. The evaluation method is as follows.

(Characteristic Temperature)

The viscosity was measured by a platinum ball-drawing method, andrespective temperatures at which the viscosity was 10² dPa·s, 10^(2.5)dPa·s, and 10³ dPa·s were determined as T2, T2.5, and T3, respectively.

(Devitrification Temperature)

The glass specimens were each crushed into particles, and the particleswere sieved to obtain particles passing through a sieve with an aperturesize of 2.83 mm and remaining in a sieve with an aperture size of 1.00mm. The particles were washed to remove fine powder deposited on theparticles, and dried to prepare a sample for devitrification temperaturemeasurement. In a platinum boat (a lidless rectangular platinumcontainer), 25 g of the sample for devitrification temperaturemeasurement was put to have a substantially uniform thickness. Afterbeing held in a temperature-gradient furnace for 2 hours, the sample wastaken out of the furnace. The highest temperature at whichdevitrification was observed inside the glass was determined as thedevitrification temperature.

(Permittivity and Dielectric Loss Tangent)

The permittivity (dielectric constant) and the dielectric loss tangentat the respective frequencies were measured using a permittivitymeasuring apparatus by a cavity resonator perturbation method. Themeasurement temperature was set to 25° C., and the dimensions of thesample for measurement were set to a rectangular parallelepiped with alength of 10 cm having a square bottom surface of side 1.5 cm.

The glass compositions of Examples 1 to 44 and 48 to 99 had apermittivity of 4.65 or less at a measurement frequency of 1 GHz, andhad T2 of 1700° C. or less and T3 of 1450° C. or less. Some of theseglass compositions had a permittivity of 4.4 or less at a measurementfrequency of 1 GHz, and the glass compositions of Examples 1 to 43, 48to 81, 83 to 84, and 93 to 99 had a permittivity of 4.36 or less at ameasurement frequency of 1 GHz. The glass compositions of Examples 1 to41, 48 to 81, 83 to 84, and 94 to 99 had a permittivity of 4.35 or lessat a measurement frequency of 1 GHz. Further, the glass compositions ofExamples 5 to 6, 66 to 67, and 83 to 92 had T2 of 1520° C. or less andT3 of 1300° C. or less that were higher than TL. The glass compositionsof Examples 66 to 67 and 83 to 92 had a B2O3 content of 35% or less, or30% or less in some cases, and had T2 of 1520° C. or less and T3 of1300° C. or less that were higher than TL. The glass compositions ofExamples 2 and 93 to 99 had a dielectric loss tangent of less than 0.001at a frequency of 1 GHz. The glass compositions of Examples 93 to 99 hada dielectric loss tangent of less than 0.001 at a frequency of 1 GHz,and had T2 of less than 1600° C. The glass compositions of Examples 45to 47 are comparative examples, and Example 45 had T2 of more than 1700°C. and Examples 46 to 47 had a permittivity of more than 4.7 at ameasurement frequency of 1 GHz.

TABLE 1 Sample No. wt % 1 2 3 4 5 6 7 8 SiO₂ 55.01 55.20 57.01 53.2146.21 48.01 51.21 51.21 B₂O₃ 33.00 33.00 32.00 32.00 38.00 38.00 34.5036.40 Al₂O₃ 6.00 6.00 5.00 5.00 7.00 7.00 7.00 8.00 Li₂O 0.09 0.09 0.900.09 0.09 0.09 0.09 0.09 Na₂O 0.09 0.09 0.30 0.09 0.09 0.09 0.09 0.09K₂O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 4.17 4.11 2.05 6.87 5.874.07 4.37 1.47 CaO 1.45 1.45 2.55 2.55 2.55 2.55 2.55 2.55 SrO 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 Fe₂O₃ 0.19 0.06 0.19 0.19 0.19 0.19 0.19 0.19 SiO₂ + B₂O₃ + Al₂O₃94.0 94.2 94.0 90.2 91.2 93.0 92.7 95.6 SiO₂ + B₂O₃ 88.0 88.2 89.0 85.284.2 86.0 85.7 87.6 (SiO₂ + B₂O₃ + Al₂O₃)/ 1.07 1.07 1.06 1.06 1.08 1.081.08 1.09 (SiO₂ + B₂O₃) RO 5.6 5.6 4.6 9.4 8.4 6.6 6.9 4.0 R₂O 0.2 0.21.2 0.2 0.2 0.2 0.2 0.2 MgO/RO 0.74 0.74 0.45 0.73 0.70 0.61 0.63 0.37T2 (° C.) 1617 1615 1639 1569 1465 1511 1555 1581 T2.5 (° C.) 1469 14711496 1416 1322 1368 1410 1441 T3 (° C.) 1348 1352 1363 1300 1218 12591297 1325 Devitrification <1160 <1160 <1160 <1160 <1160 <1160 <1160 1059temperature TL (° C.) Permittivity (1 GHz) 4.08 4.07 4.19 4.33 4.31 4.184.21 4.03 Dielectric loss 0.0011 0.0008 0.0022 0.0010 0.0018 0.00180.0014 0.0016 tangent (1 GHz) Permittivity (5 GHz) 4.05 4.04 4.16 4.314.28 4.15 4.18 3.99 Dielectric loss 0.0009 0.0008 0.0005 0.0014 0.00100.0007 0.0011 0.0019 tangent (5 GHz) Permittivity (10 GHz) 3.95 3.944.06 4.22 4.19 4.05 4.09 3.89 Dielectric loss 0.0013 0.0011 0.00090.0007 0.0014 0.0012 0.0005 0.0023 tangent (10 GHz) Sample No. wt % 9 1011 12 13 14 15 SiO₂ 51.91 51.20 51.91 50.75 50.88 51.72 52.39 B₂O₃ 31.0031.00 31.00 34.88 33.91 33.34 31.88 Al₂O₃ 13.30 14.70 12.50 10.84 10.8711.63 11.67 Li₂O 0.30 0.30 0.30 0.09 0.09 0.09 0.09 Na₂O 0.09 0.09 0.090.09 0.09 0.09 0.09 K₂O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.66 1.221.46 0.61 0.77 1.23 1.54 CaO 2.55 1.30 2.55 2.55 3.20 1.71 2.14 SrO 0.000.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00Fe₂O₃ 0.19 0.19 0.19 0.19 0.19 0.19 0.20 SiO₂ + B₂O₃ + Al₂O₃ 96.2 96.995.4 96.5 95.7 96.7 95.9 SiO₂ + B₂O₃ 82.9 82.2 82.9 85.6 84.8 85.1 84.3(SiO₂ + B₂O₃ + Al₂O₃)/ 1.16 1.18 1.15 1.13 1.13 1.14 1.14 (SiO₂ + B₂O₃)RO 3.2 2.5 4.0 3.2 4.0 2.9 3.7 R₂O 0.4 0.4 0.4 0.2 0.2 0.2 0.2 MgO/RO0.21 0.48 0.36 0.19 0.19 0.42 0.42 T2 (° C.) 1563 1536 1558 1557 15701571 1579 T2.5 (° C.) 1437 1416 1430 1432 1436 1440 1447 T3 (° C.) 13291312 1321 1325 1326 1331 1338 Devitrification 1317 1442 1191 1277 <11601324 1250 temperature TL (° C.) Permittivity (1 GHz) 4.22 4.20 4.25 4.074.14 4.07 4.14 Dielectric loss 0.0019 0.0020 0.0019 0.0018 0.0017 0.00170.0016 tangent (1 GHz) Permittivity (5 GHz) 4.19 4.17 4.23 4.04 4.114.04 4.11 Dielectric loss 0.0029 0.0031 0.0024 0.0027 0.0024 0.00240.0021 tangent (5 GHz) Permittivity (10 GHz) 4.10 4.08 4.13 3.93 4.013.94 4.02 Dielectric loss 0.0034 0.0036 0.0028 0.0031 0.0029 0.00290.0025 tangent (10 GHz)

TABLE 2 Sample No. wt % 16 17 18 19 20 21 22 23 24 SiO₂ 52.15 50.8751.72 51.70 53.81 53.00 52.50 50.04 50.02 B₂O₃ 31.86 34.96 33.33 33.3331.91 31.00 31.42 33.93 37.12 Al₂O₃ 11.99 10.86 11.62 11.62 10.90 12.0012.14 12.10 9.32 Li₂O 0.20 0.09 0.07 0.05 0.05 0.20 0.10 0.10 0.09 Na₂O0.10 0.09 0.14 0.19 0.19 0.10 0.13 0.13 0.09 K₂O 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 MgO 1.50 1.23 1.23 1.22 1.23 1.50 0.53 0.530.61 CaO 2.00 1.71 1.70 1.70 1.71 2.00 2.98 2.97 2.56 SrO 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 Fe₂O₃ 0.20 0.19 0.19 0.19 0.20 0.20 0.20 0.20 0.19 SiO₂ +B₂O₃ + Al₂O₃ 96.0 96.7 96.7 96.6 96.6 96.0 96.1 96.1 96.4 SiO₂ + B₂O₃84.0 85.8 85.0 85.0 85.7 84.0 83.9 84.0 87.1 (SiO₂ + B₂O₃ + Al₂O₃)/ 1.141.13 1.14 1.14 1.13 1.14 1.15 1.14 1.11 (SiO₂ + B₂O₃) RO 3.5 2.9 2.9 2.92.9 3.5 3.5 3.5 3.2 R₂O 0.3 0.2 0.2 0.2 0.2 0.3 0.2 0.2 0.2 MgO/RO 0.430.42 0.42 0.42 0.42 0.43 0.15 0.15 0.19 T2 (° C.) 1560 1562 1570 15711594 1568 1592 1553 1566 T2.5 (° C.) 1428 1431 1437 1440 1462 1445 14611424 1431 T3 (° C.) 1320 1321 1329 1331 1350 1340 1351 1317 1318Devitrification 1290 1295 1309 1329 1312 1280 1308 1310 1218 temperatureTL (° C.) Permittivity (1 GHz) 4.17 4.04 4.07 4.07 4.06 4.17 4.17 4.154.01 Dielectric loss 0.0018 0.0018 0.0017 0.0017 0.0012 0.0017 0.00170.0020 0.0019 tangent (1 GHz) Permittivity (5 GHz) 4.13 4.01 4.04 4.044.02 4.14 4.14 4.12 3.97 Dielectric loss 0.0023 0.0025 0.0022 0.00200.0016 0.0022 0.0024 0.0027 0.0026 tangent (5 GHz) Permittivity (10 GHz)4.04 3.91 3.91 3.94 3.92 4.04 4.04 4.02 3.87 Dielectric loss 0.00280.0029 0.0020 0.0024 0.0021 0.0022 0.0028 0.0032 0.0031 tangent (10 GHz)Sample No. wt % 25 26 27 28 29 30 31 SiO₂ 51.00 51.74 49.76 52.10 49.5151.26 49.28 B₂O₃ 36.12 33.87 35.89 32.76 37.45 34.17 36.20 Al₂O₃ 9.3310.85 10.82 11.61 7.84 9.38 9.36 Li₂O 0.09 0.09 0.09 0.09 0.09 0.09 0.09Na₂O 0.09 0.09 0.09 0.09 0.10 0.10 0.09 K₂O 0.00 0.00 0.00 0.00 0.000.00 0.00 MgO 0.61 0.61 0.61 0.61 0.93 0.93 0.92 CaO 2.57 2.56 2.55 2.553.88 3.87 3.86 SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.000.00 0.00 0.00 0.00 0.00 Fe₂O₃ 0.19 0.19 0.19 0.19 0.20 0.20 0.20 SiO₂ +B₂O₃ + Al₂O₃ 96.4 96.4 96.5 96.5 94.8 94.8 94.8 SiO₂ + B₂O₃ 87.1 85.685.6 84.8 87.0 85.4 85.5 (SiO₂ + B₂O₃ + Al₂O₃)/ 1.11 1.13 1.13 1.14 1.091.11 1.11 (SiO₂ + B₂O₃) RO 3.2 3.2 3.2 3.2 4.8 4.8 4.8 R₂O 0.2 0.2 0.20.2 0.2 0.2 0.2 MgO/RO 0.19 0.19 0.19 0.19 0.19 0.19 0.19 T2 (° C.) 15811583 1552 1584 1567 1585 1554 T2.5 (° C.) 1445 1450 1421 1453 1427 14471417 T3 (° C.) 1331 1338 1312 1342 1313 1333 1306 Devitrification 12181276 1277 1305 <1160 <1160 <1160 temperature TL (° C.) Permittivity (1GHz) 4.01 4.07 4.06 4.10 4.09 4.16 4.15 Dielectric loss 0.0018 0.00170.0019 0.0016 0.0018 0.0017 0.0019 tangent (1 GHz) Permittivity (5 GHz)3.98 4.04 4.03 4.07 4.06 4.13 4.12 Dielectric loss 0.0025 0.0025 0.00280.0025 0.0021 0.0020 0.0023 tangent (5 GHz) Permittivity (10 GHz) 3.883.94 3.93 3.97 3.96 4.03 4.02 Dielectric loss 0.0030 0.0030 0.00330.0030 0.0026 0.0025 0.0028 tangent (10 GHz)

TABLE 3 Sample No. wt % 32 33 34 35 36 37 38 39 40 SiO₂ 51.12 51.8749.89 50.65 49.23 55.30 56.50 57.45 52.83 B₂O₃ 35.15 32.90 34.92 35.4642.56 28.25 29.17 26.36 30.54 Al₂O₃ 9.36 10.88 10.85 7.87 6.23 11.2012.37 12.22 13.11 Li₂O 0.09 0.09 0.09 0.09 0.09 0.10 0.09 0.10 0.09 Na₂O0.09 0.09 0.09 0.10 0.09 0.14 0.09 0.14 0.09 K₂O 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 MgO 0.77 0.77 0.77 1.09 0.31 0.54 0.31 0.530.61 CaO 3.22 3.21 3.20 4.54 1.29 4.27 1.28 3.00 2.54 SrO 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 Fe₂O₃ 0.20 0.19 0.19 0.20 0.20 0.20 0.19 0.20 0.19 SiO₂ +B₂O₃ + 95.6 95.6 95.7 94.0 98.0 94.7 98.0 96.0 96.5 Al₂O₃ SiO₂ + B₂O₃86.3 84.8 84.8 86.1 91.8 83.5 85.7 83.8 83.4 (SiO₂ + B₂O₃ + 1.11 1.131.13 1.09 1.07 1.13 1.14 1.15 1.16 Al₂O₃)/(SiO₂ + B₂O₃) RO 4.0 4.0 4.05.6 1.6 4.8 1.6 3.5 3.2 R₂O 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 MgO/RO0.19 0.19 0.19 0.19 0.19 0.11 0.19 0.15 0.19 T2 (° C.) 1583 1585 15541584 1574 1642 1650 1669 1586 T2.5 (° C.) 1446 1451 1422 1442 1434 15061518 1534 1458 T3 (° C.) 1332 1339 1312 1327 1315 1390 1402 1418 1349Devitrification <1160 1198 1199 <1160 1257 <1160 1487 1305 1363temperature TL (° C.) Permittivity 4.09 4.15 4.14 4.17 3.74 4.26 4.014.19 4.17 (1 GHz) Dielectric 0.0017 0.0016 0.0018 0.0017 0.0020 0.00130.0012 0.0011 0.0016 loss tangent (1 GHz) Permittivity 4.05 4.12 4.114.14 3.70 4.23 3.98 4.16 4.14 (5 GHz) Dielectric 0.0023 0.0023 0.00260.0018 0.0029 0.0016 0.0024 0.0017 0.0026 loss tangent (5 GHz)Permittivity 3.95 4.02 4.01 4.05 3.59 4.14 3.87 4.07 4.04 (10 GHz)Dielectric 0.0027 0.0028 0.0030 0.0022 0.0034 0.0021 0.0029 0.00210.0030 loss tangent (10 GHz) Sample No. wt % 41 42 43 44 45 46 47 SiO₂40.46 51.99 53.23 52.00 62.00 52.00 38.00 B₂O₃ 41.56 27.00 25.81 25.0025.00 27.00 35.00 Al₂O₃ 12.94 17.06 17.06 16.00 8.00 10.00 15.00 Li₂O0.09 0.10 0.10 0.10 0.10 0.10 0.10 Na₂O 0.09 0.15 0.15 0.15 0.15 0.150.14 K₂O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.90 0.57 0.52 1.56 1.625.56 7.29 CaO 3.77 2.94 2.94 5.00 2.94 5.00 4.27 SrO 0.00 0.00 0.00 0.000.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe₂O₃ 0.19 0.190.19 0.19 0.19 0.19 0.20 SiO₂ + B₂O₃ + 95.0 96.1 96.1 93.0 95.0 89.088.0 Al₂O₃ SiO₂ + B₂O₃ 82.0 79.0 79.0 77.0 87.0 79.0 73.0 (SiO₂ + B₂O₃ +1.16 1.22 1.22 1.21 1.09 1.13 1.21 Al₂O₃)/(SiO₂ + B₂O₃) RO 4.7 3.5 3.56.6 4.6 10.6 11.6 R₂O 0.2 0.2 0.2 0.2 0.2 0.2 0.2 MgO/RO 0.19 0.16 0.150.24 0.36 0.53 0.63 T2 (° C.) 1389 1553 1570 1550 1739 1540 1287 T2.5 (°C.) 1268 1435 1450 1426 1591 1398 1165 T3 (° C.) 1176 1335 1348 13251461 1291 1091 Devitrification 1216 1505 1506 <1160 973 <1160 <1160temperature TL (° C.) Permittivity 4.24 4.36 4.36 4.58 4.13 4.72 5.04 (1GHz) Dielectric 0.0029 0.0018 0.0016 0.0016 0.0005 0.0012 0.0027 losstangent (1 GHz) Permittivity 4.21 4.34 4.34 4.57 4.10 4.71 5.04 (5 GHz)Dielectric 0.0038 0.0028 0.0026 0.0016 0.0010 0.0009 0.0004 loss tangent(5 GHz) Permittivity 4.12 4.25 4.25 4.48 4.00 4.64 4.97 (10 GHz)Dielectric 0.0043 0.0032 0.0031 0.0021 0.0004 0.0013 0.0008 loss tangent(10 GHz) *Examples 45 to 47 are comparative examples.

TABLE 4 Sample No. wt % 48 49 50 51 52 53 54 55 56 SiO₂ 54.00 54.0053.00 54.00 52.84 52.47 52.71 52.32 52.84 B₂O₃ 30.00 31.00 29.35 30.0030.91 30.70 30.83 30.89 30.91 Al₂O₃ 12.10 11.00 12.85 12.00 11.97 13.7013.17 12.81 11.97 Li₂O 0.10 0.10 0.12 0.20 0.20 0.20 0.36 0.20 0.20 Na₂O0.10 0.07 0.11 0.10 0.10 0.10 0.10 0.10 0.10 K₂O 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 MgO 0.50 0.87 0.81 3.00 0.75 1.10 1.10 1.500.75 CaO 3.00 2.76 3.56 0.50 3.03 1.53 1.53 1.99 3.03 SrO 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 Fe₂O₃ 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.19 0.20 SiO₂ +B₂O₃ + 96.1 96.0 95.2 96.0 95.7 96.9 96.7 96.0 95.7 Al₂O₃ SiO₂ + B₂O₃84.0 85.0 82.4 84.0 83.8 83.2 83.5 83.2 83.8 (SiO₂ + B₂O₃ + 1.14 1.131.16 1.14 1.14 1.16 1.16 1.15 1.14 Al₂O₃)/(SiO₂ + B₂O₃) RO 3.5 3.6 4.43.5 3.8 2.6 2.6 3.5 3.8 R₂O 0.2 0.2 0.2 0.3 0.3 0.3 0.5 0.3 0.3 MgO/RO0.14 0.24 0.19 0.86 0.20 0.42 0.42 0.43 0.20 T2 (° C.) 1628 1675 15961593 1596 1573 1574 1567 1596 T2.5 (° C.) 1490 1518 1469 1463 1465 14481449 1439 1465 T3 (° C.) 1378 1395 1361 1354 1354 1342 1340 1331 1354Devitrification 1283 1284 1261 1280 1267 1444 1381 1285 1267 temperatureTL (° C.) Permittivity 4.17 4.13 4.27 4.18 4.17 4.16 4.18 4.20 4.20 (1GHz) Dielectric 0.0012 0.0014 0.0016 0.0014 0.0013 0.0018 0.0020 0.00170.0017 loss tangent (1 GHz) Permittivity 4.14 4.10 4.25 4.12 4.17 4.134.15 4.17 4.17 (5 GHz) Dielectric 0.0024 0.0022 0.0022 0.0015 0.00250.0028 0.0029 0.0023 0.0025 loss tangent (5 GHz) Permittivity 4.05 4.004.15 4.07 4.03 4.03 4.05 4.08 4.08 (10 GHz) Dielectric 0.0023 0.00270.0027 0.0024 0.0022 0.0032 0.0033 0.0028 0.0029 loss tangent (10 GHz)Sample No. wt % 57 58 59 60 61 62 63 SiO₂ 52.86 53.10 53.20 53.01 53.2653.21 53.04 B₂O₃ 30.39 30.74 31.13 30.69 31.15 31.12 31.02 Al₂O₃ 12.7512.02 11.48 12.00 10.96 10.94 11.69 Li₂O 0.20 0.34 0.37 0.20 0.20 0.200.29 Na₂O 0.10 0.10 0.10 0.10 0.10 0.10 0.10 K₂O 0.00 0.00 0.00 0.000.00 0.00 0.00 MgO 1.50 1.50 1.51 1.38 1.51 1.24 1.11 CaO 2.00 2.00 2.012.42 2.62 2.99 2.55 SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.000.00 0.00 0.00 0.00 0.00 0.00 Fe₂O₃ 0.20 0.20 0.20 0.20 0.20 0.20 0.20SiO₂ + B₂O₃ + 96.0 95.9 95.8 95.7 95.4 95.3 95.8 Al₂O₃ SiO₂ + B₂O₃ 83.383.8 84.3 83.7 84.4 84.3 84.1 (SiO₂ + B₂O₃ + 1.15 1.14 1.14 1.14 1.131.13 1.14 Al₂O₃)/(SiO₂ + B₂O₃) RO 3.5 3.5 3.8 4.1 4.2 3.7 R₂O 0.3 0.40.5 0.3 0.3 0.3 0.4 MgO/RO 0.43 0.43 0.43 0.36 0.37 0.29 0.30 T2 (° C.)1583 1585 1587 1591 1601 1603 1591 T2.5 (° C.) 1454 1456 1448 1461 14671469 1455 T3 (° C.) 1346 1346 1334 1351 1355 1357 1345 Devitrification1319 1256 1228 1262 1190 1182 1251 temperature TL (° C.) Permittivity4.20 4.21 4.17 4.20 4.19 4.20 4.17 (1 GHz) Dielectric 0.0017 0.00190.0015 0.0017 0.0016 0.0017 0.0014 loss tangent (1 GHz) Permittivity4.17 4.18 4.16 4.17 4.16 4.17 4.17 (5 GHz) Dielectric 0.0023 0.00240.0023 0.0022 0.0020 0.0021 0.0024 loss tangent (5 GHz) Permittivity4.08 4.08 4.05 4.07 4.06 4.07 4.03 (10 GHz) Dielectric 0.0028 0.00280.0025 0.0027 0.0024 0.0025 0.0024 loss tangent (10 GHz)

TABLE 5 Sample No. wt % 64 65 66 67 68 69 70 71 72 73 SiO₂ 49.95 49.9049.70 49.36 49.83 49.18 51.59 51.83 51.87 51.98 B₂O₃ 33.44 33.75 34.1334.94 34.21 34.50 33.25 33.40 33.44 33.51 Al₂O₃ 12.43 12.01 11.76 11.3211.32 11.99 11.60 11.18 10.88 10.59 Li₂O 0.10 0.24 0.31 0.34 0.24 0.240.07 0.20 0.30 0.39 Na₂O 0.10 0.10 0.10 0.10 0.10 0.10 0.14 0.14 0.140.14 K₂O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.80 0.810.81 0.80 0.81 0.81 0.61 0.92 0.61 0.62 CaO 2.99 3.00 3.00 2.95 3.302.99 2.55 2.14 2.57 2.57 SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Fe₂O₃0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.20 SiO₂ + B₂O₃ + 95.895.7 95.6 95.6 95.4 95.7 96.4 96.4 96.2 96.1 Al₂O₃ SiO₂ + B₂O₃ 83.4 83.783.8 84.3 84.0 83.7 84.8 85.2 85.3 85.5 (SiO₂ + B₂O₃ + 1.15 1.14 1.141.13 1.14 1.14 1.14 1.13 1.13 1.12 Al₂O₃)/(SiO₂ + B₂O₃) RO 3.8 3.8 3.83.7 4.1 3.8 3.2 3.1 3.2 3.2 R₂O 0.2 0.3 0.4 0.4 0.3 0.3 0.2 0.4 0.4 0.5MgO/RO 0.21 0.21 0.21 0.21 0.20 0.21 0.19 0.30 0.19 0.19 T2 (° C.) 15441540 1509 1515 1544 1529 1577 1574 1575 1576 T2.5 (° C.) 1415 1412 13911387 1414 1401 1446 1443 1447 1446 T3 (° C.) 1309 1305 1289 1281 13051295 1335 1331 1338 1331 Devitrification 1273 1222 1223 1174 1166 12221308 1266 1240 1188 temperature TL (° C.) Permittivity 4.19 4.20 4.214.17 4.20 4.20 4.10 4.10 4.10 4.14 (1 GHz) Dielectric 0.0019 0.00210.0014 0.0014 0.0020 0.0021 0.0017 0.0019 0.0013 0.0021 loss tangent (1GHz) Permittivity 4.16 4.17 4.18 4.16 4.17 4.17 4.07 4.07 4.10 4.11 (5GHz) Dielectric 0.0027 0.0028 0.0029 0.0029 0.0027 0.0029 0.0024 0.00240.0025 0.0026 loss tangent (5 GHz) Permittivity 4.06 4.08 4.09 4.05 4.084.07 3.97 3.97 3.99 4.01 (10 GHz) Dielectric 0.0031 0.0033 0.0023 0.00230.0031 0.0034 0.0029 0.0028 0.0022 0.0031 loss tangent (10 GHz) SampleNo. wt % 74 75 76 77 78 79 80 81 SiO₂ 54.03 53.91 51.92 51.77 52.8754.68 50.95 52.01 B₂O₃ 32.05 31.98 33.48 33.36 32.80 30.28 29.71 30.34Al₂O₃ 10.17 10.46 10.90 11.17 10.61 11.67 16.03 11.69 Li₂O 0.28 0.180.30 0.20 0.30 0.05 0.04 0.05 Na₂O 0.19 0.19 0.14 0.14 0.14 0.19 0.190.19 K₂O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 0.93 0.93 0.92 0.610.93 1.23 1.21 1.23 CaO 2.15 2.15 2.14 2.56 2.15 1.71 1.68 4.29 SrO 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 Fe₂O₃ 0.20 0.20 0.20 0.19 0.20 0.19 0.19 0.20 SiO₂ + B₂O₃ +96.3 96.4 96.3 96.3 96.3 96.6 96.7 94.0 Al₂O₃ SiO₂ + B₂O₃ 86.1 85.9 85.485.1 85.7 85.0 80.7 82.4 (SiO₂ + B₂O₃ + 1.12 1.12 1.13 1.13 1.12 1.141.20 1.14 Al₂O₃)/(SiO₂ + B₂O₃) RO 3.1 3.1 3.1 3.2 3.1 2.9 2.9 5.5 R₂O0.5 0.4 0.4 0.4 0.4 0.2 0.2 0.2 MgO/RO 0.30 0.30 0.30 0.19 0.30 0.420.42 0.22 T2 (° C.) 1611 1611 1574 1566 1588 1618 1531 1580 T2.5 (° C.)1477 1477 1443 1434 1456 1485 1412 1447 T3 (° C.) 1360 1362 1330 13261343 1371 1312 1337 Devitrification 1203 1238 1247 1296 1219 1327 15061081 temperature TL (° C.) Permittivity 4.10 4.09 4.09 4.08 4.11 4.094.24 4.31 (1 GHz) Dielectric 0.0018 0.0017 0.0014 0.0012 0.0020 0.00140.0018 0.0016 loss tangent (1 GHz) Permittivity 4.06 4.05 4.08 4.09 4.084.05 4.21 4.29 (5 GHz) Dielectric 0.0019 0.0018 0.0024 0.0025 0.00200.0016 0.0024 0.0014 loss tangent (5 GHz) Permittivity 3.97 3.95 3.973.95 3.98 3.96 4.12 4.20 (10 GHz) Dielectric 0.0023 0.0023 0.0021 0.00200.0030 0.0020 0.0029 0.0018 loss tangent (10 GHz)

TABLE 6 Sample No. wt % 82 83 84 85 86 87 88 89 90 SiO₂ 50.79 49.7049.35 49.71 49.48 49.40 49.40 49.40 49.40 B₂O₃ 27.95 34.13 34.95 29.0629.09 29.68 28.25 27.80 28.00 Al₂O₃ 14.47 11.76 11.32 14.45 14.46 13.9716.35 16.65 16.80 Li₂O 0.17 0.31 0.34 0.17 0.17 0.32 0.20 0.20 0.20 Na₂O0.13 0.10 0.10 0.13 0.13 0.13 0.13 0.13 0.13 K₂O 0.00 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 MgO 1.50 0.81 0.80 1.50 1.68 1.50 1.50 1.501.50 CaO 4.80 3.00 2.95 4.79 4.80 4.81 3.98 4.13 3.78 SrO 0.00 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 TiO₂ 0.00 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 Fe₂O₃ 0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.19 0.19 SiO₂ +B₂O₃ + 93.2 95.6 95.6 93.2 93.0 93.0 94.0 93.9 94.2 Al₂O₃ SiO₂ + B₂O₃78.7 83.8 84.3 78.8 78.6 79.1 77.7 77.2 77.4 (SiO₂ + B₂O₃ + 1.18 1.141.13 1.18 1.18 1.18 1.21 1.22 1.22 Al₂O₃)/ (SiO₂ + B₂O₃) RO 6.3 3.8 3.76.3 6.5 6.3 5.5 5.6 5.3 R₂O 0.3 0.4 0.4 0.3 0.3 0.5 0.3 0.3 0.3 MgO/RO0.24 0.21 0.21 0.24 0.26 0.24 0.27 0.27 0.28 T2 (° C.) 1533 1509 15151496 1498 1485 1502 1505 1495 T2.5 (° C.) 1405 1391 1387 1382 1382 13681389 1388 1376 T3 (° C.) 1301 1289 1281 1286 1286 1269 1293 1291 1280Devitrification 1223 <1169 <1169 <1169 1006 1290 1274 1247 temperatureTL (° C.) Permittivity 4.61 4.31 4.29 4.60 4.62 4.62 4.60 4.63 4.61 (1GHz) Dielectric 0.0017 0.0023 0.0024 0.0018 0.0019 0.0021 0.0017 0.00180.0021 loss tangent (1 GHz) Permittivity 4.59 4.28 4.26 4.58 4.60 4.604.60 4.62 4.59 (5 GHz) Dielectric 0.0016 0.0028 0.0029 0.0018 0.00170.0020 0.0024 0.0024 0.0025 loss tangent (5 GHz) Permittivity 4.51 4.184.17 4.50 4.51 4.52 4.50 4.51 4.51 (10 GHz) Dielectric 0.0023 0.00360.0037 0.0026 0.0024 0.0028 0.0032 0.0032 0.0033 loss tangent (10 GHz)Sample No. wt % 91 92 93 94 95 96 97 98 99 SiO₂ 49.37 49.40 50.70 50.7051.20 49.29 49.63 50.25 50.16 B₂O₃ 28.48 28.00 31.20 31.20 31.20 32.4332.48 31.87 31.93 Al₂O₃ 15.89 16.30 14.20 13.40 13.70 12.62 13.24 13.2213.25 Li₂O 0.20 0.20 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Na₂O 0.19 0.130.05 0.05 0.05 0.05 0.05 0.05 0.05 K₂O 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 MgO 1.50 1.50 0.50 0.50 0.50 0.49 0.49 0.49 0.49 CaO 4.184.28 1.30 1.30 1.00 1.78 1.70 1.32 1.70 SrO 0.00 0.00 1.70 1.70 2.003.09 2.16 2.55 2.17 TiO₂ 0.00 0.00 0.00 0.80 0.00 0.00 0.00 0.00 0.00Fe₂O₃ 0.19 0.19 0.20 0.20 0.20 0.10 0.10 0.10 0.10 SiO₂ + B₂O₃ + 93.893.7 95.7 95.3 96.1 94.3 95.3 95.3 95.3 Al₂O₃ SiO₂ + B₂O₃ 77.9 77.4 81.581.9 82.4 81.7 82.1 82.1 82.1 (SiO₂ + B₂O₃ + 1.20 1.21 1.17 1.16 1.171.15 1.16 1.16 1.16 Al₂O₃)/ (SiO₂ + B₂O₃) RO 5.7 5.8 3.5 3.5 3.5 5.4 4.44.4 4.4 R₂O 0.4 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 MgO/RO 0.26 0.26 0.140.14 0.14 0.09 0.11 0.11 0.13 T2 (° C.) 1500 1498 1563 1571 1583 15621555 1572 1578 T2.5 (° C.) 1380 1378 1423 1417 1460 1429 1424 1440 1451T3 (° C.) 1281 1280 1328 1326 1351 1319 1317 1330 1342 Devitrification1168 1175 1369 1352 1363 1258 1312 1332 1301 temperature TL (° C.)Permittivity 4.61 4.64 4.36 4.26 4.26 4.32 4.28 4.30 4.30 (1 GHz)Dielectric 0.0022 0.0020 0.0009 0.0008 0.0007 0.0009 0.0009 0.00080.0008 loss tangent (1 GHz) Permittivity 4.59 4.62 4.33 4.23 4.23 4.294.25 4.27 4.27 (5 GHz) Dielectric 0.0024 0.0023 0.0017 0.0016 0.00150.0012 0.0015 0.0014 0.0014 loss tangent (5 GHz) Permittivity 4.51 4.544.25 4.09 4.18 4.16 4.15 4.18 4.17 (10 GHz) Dielectric 0.0032 0.00310.0022 0.0021 0.0020 0.0022 0.0021 0.0023 0.0021 loss tangent (10 GHz)

1.-65. (canceled)
 66. A glass composition comprising, in wt %:40≤SiO₂≤60; 29≤B₂O₃≤45; 5≤Al₂O₂≤15; 0<R₂O≤5; 1≤RO<15; and 0≤ZnO≤1,wherein the glass composition satisfies: SiO₂+B₂O₃≥80,0.1≤MgO/(MgO+CaO)≤0.5; and/or SiO₂+B₂O₃≥78, 1≤RO<10, and0.1≤MgO/(MgO+CaO)≤0.5, where R₂O is at least one oxide selected fromLi₂O, Na₂O, and K₂O, and RO is at least one oxide selected from MgO,CaO, and SrO.
 67. A glass composition, satisfying, in wt %,SiO₂+B₂O₃≥77, wherein a permittivity at a frequency of 1 GHz is 4.4 orless, a dielectric loss tangent at a frequency of 1 GHz is 0.007 orless, and a temperature T2 at which a viscosity is 10² dPas is 1700° C.or less.
 68. The glass composition according to claim 67, comprising, inwt %: 40≤SiO₂<58; 25≤B₂O₃≤40; 7.5≤Al₂O₃≤18; 0<R₂O≤4; 0≤Li₂O≤1.5;0≤Na₂O≤1.5; 0≤K₂O≤1; 1≤RO<10; 0≤MgO<10; 0≤CaO<10; 0≤SrO≤5; and0≤T-Fe₂O₃≤0.5, where R₂O is at least one oxide selected from Li₂O, Na₂O,and K₂O, RO is at least one oxide selected from MgO, CaO, and SrO, andT-Fe₂O₃ is total iron oxide calculated as Fe₂O₃ in the glasscomposition.
 69. The glass composition according to claim 67,comprising, in wt %, 0.01≤T-Fe₂O₃≤0.5.
 70. The glass compositionaccording to claim 67, being substantially free of BaO and PbO.
 71. Theglass composition according to claim 67, being substantially free ofTiO₂.
 72. The glass composition according to claim 67, comprising, in wt%, 0<TiO₂≤1.
 73. The glass composition according to claim 67, wherein apermittivity at a frequency of 1 GHz is 4.35 or less, and a dielectricloss tangent at a frequency of 1 GHz is 0.005 or less.
 74. The glasscomposition according to claim 67, wherein a temperature T2 at which aviscosity is 10² dPas is 1650° C. or less.
 75. The glass compositionaccording to claim 67, wherein a temperature T3 at which a viscosity is10³ dPas is 1365° C. or less.
 76. The glass composition according toclaim 67, wherein a temperature T3 at which a viscosity is 10³ dPas ishigher than a devitrification temperature TL.
 77. A glass fibercomprising the glass composition according to claim
 66. 78. A glasscloth comprising the glass fiber according to claim
 77. 79. A prepregcomprising the glass cloth according to claim
 78. 80. A printed boardcomprising the glass cloth according to claim
 78. 81. A method forproducing a glass fiber, the method comprising melting the glasscomposition according to claim 67 at a temperature of 1400° C. or moreto obtain a glass fiber having an average fiber diameter of 1 to 6 μm.82. The glass composition according to claim 67, comprising, in wt %,SnO₂<0.5.
 83. The glass composition according to claim 67, comprising,in wt %, BaO<0.5.
 84. The glass composition according to claim 67,comprising, in wt %, 49≤SiO₂<55.
 85. The glass composition according toclaim 67, comprising, in wt %, 27≤B₂O₃≤32.
 86. The glass compositionaccording to claim 67, comprising, in wt %, 10≤Al₂O₃≤14.
 87. A glassfiber comprising the glass composition according to claim
 67. 88. Aglass cloth comprising the glass fiber according to claim
 87. 89. Aprepreg comprising the glass cloth according to claim
 88. 90. A printedboard comprising the glass cloth according to claim 88.